The following prior U.S. patents are believed to be indicative of past efforts in this field of endeavor. The Stokes and Fisher (U.S. Pat. No. 1,954,461, issued Apr. 10, 1934, and No. 3,797,468, issued Mar. 19, 1974), patents disclose, respectively, fluid-heat-exchanger tubes between a carburetor and an intake manifold; the Silverstein (U.S. Pat. No. 2,179,235, issued Nov. 7, 1939) patent discloses using exhaust gases to heat an air-fuel mixture; the Christian (U.S. Pat. No. 3,042,016, issued July 3, 1962) patent discloses small pipes surrounded by a heavy metal container heated by the exhaust manifold; the Terao (U.S. Pat. No. 3,107,660, issued Oct. 22, 1963) patent discloses a plurality of perforated walls and passages made of high heat conductive materials; and, the Dillow (U.S. Pat. No. 3,780,714, issued Dec. 25, 1973) patent disclosing tubing wholly housed within an engine manifold.